Method and apparatus for searching for signals in a wireless communication system

ABSTRACT

Techniques to search for signals while in an out-of-service state are described. In an aspect, a network entity may collect information for wireless devices within a designated area, determine at least one search parameter (e.g., a scan rate) based on the collected information, and provide the search parameter(s) to wireless devices within the designated area. The wireless devices may perform searches for signals in accordance with the search parameter(s) when they are out of service. In another aspect, a wireless device may collect information related to out-of-service events encountered by the wireless device, send the collected information to the network entity, receive the search parameter(s) from the network entity, and perform searches in accordance with the search parameter(s) when out of service. In yet another aspect, the wireless device may determine the search parameter(s) based on the collected information.

BACKGROUND

I. Field

The present disclosure relates generally to communication, and morespecifically to techniques for searching for signals in a wirelesscommunication system.

II. Background

Wireless communication systems are widely deployed to provide variouscommunication services such as voice, video, packet data, messaging,broadcast, etc. These systems may be multiple-access systems capable ofsupporting multiple users by sharing the available system resources.Examples of such multiple-access systems include Code Division MultipleAccess (CDMA) systems, Time Division Multiple Access (TDMA) systems,Frequency Division Multiple Access (FDMA) systems, Orthogonal FDMA(OFDMA) systems, and Single-Carrier FDMA (SC-FDMA) systems.

A wireless device (e.g., a cellular phone) may be able to receiveservice from one or more wireless communication systems. Upon power up,the wireless device may search for signals from a system from which itmay receive service. If a system is found, then the wireless device mayregister with the system. The wireless device may then activelycommunicate with the system or go into an idle mode if communication isnot required. If the wireless device subsequently loses the system, thenit may enter an out-of-service state and attempt to re-acquire a signalfrom which service may be obtained.

The wireless device may not have any knowledge of its operatingenvironment while in the out-of-service state. The wireless device maynot know whether or when it can re-acquire a signal since this maydepend on various factors such as system deployment, user mobility,channel conditions, system loading, etc. The wireless device may consumea large amount of battery power if it continuously searches for signalswhile in the out-of-service state. This heavy battery power consumptionmay significantly reduce both standby time and talk time.

SUMMARY

Techniques to efficiently search for signals while in the out-of-servicestate are described herein. In an aspect, a network entity may collectinformation for a plurality of wireless devices. The collectedinformation may comprise out-of-service durations, locations of wirelessdevices, frequency of out-of-service events, network loading, droppedcalls, weather conditions, etc. The network entity may receive theinformation from the wireless devices and/or from other network entitiessuch as base stations. The network entity may determine at least onesearch parameter based on the collected information. For example, thenetwork entity may estimate an average out-of-service time for thewireless devices based on the collected information and may determine ascan rate based on the estimated average out-of-service time. The scanrate is the rate at which a wireless device performs a search forsignals. The network entity may provide the at least one searchparameter to wireless devices for use in performing searches for signalswhen these wireless devices are out of service.

In another aspect, a wireless device may collect information related toout-of-service events encountered by the wireless device. The collectedinformation may comprise out-of-service durations, locations of thewireless device, frequency of out-of-service events, signal strength,etc. The wireless device may send the collected information to thenetwork entity. The wireless device may receive at least one searchparameter (e.g., a scan rate) determined by the network entity based oninformation collected for a plurality of wireless devices. The wirelessdevice may perform searches in accordance with the at least one searchparameter when it is out of service.

In yet another aspect, a wireless device may collect information relatedto out-of-service events encountered by the wireless device and maydetermine at least one search parameter based on the collectedinformation. The wireless device may perform searches in accordance withthe at least one search parameter when it is out of service. In onedesign, the wireless device may determine a first scan rate based on thecollected information, receive a second scan rate from the networkentity, determine a third scan rate based on the first and second scanrates, and perform searches in accordance with the third scan rate.

Various aspects and features of the disclosure are described in furtherdetail below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a wireless communication system.

FIG. 2 shows a design of periodically performing searches.

FIG. 3 shows a process for supporting searches for signals.

FIG. 4 shows an apparatus for supporting searches for signals.

FIG. 5 shows a process for operating a wireless device.

FIG. 6 shows an apparatus for operating a wireless device.

FIG. 7 shows another process for operating a wireless device.

FIG. 8 shows another apparatus for operating a wireless device.

FIG. 9 shows a block diagram of a wireless device, a base station, and anetwork entity.

DETAILED DESCRIPTION

The techniques described herein may be used for various wirelesscommunication systems such as CDMA, TDMA, FDMA, OFDMA and SC-FDMAsystems. The terms “system” and “network” are often usedinterchangeably. A CDMA system may implement a radio technology such asUniversal Terrestrial Radio Access (UTRA), cdma2000, etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. cdma2000 coversIS-2000, IS-95 and IS-856 standards. IS-2000 is also referred to asCDMA2000 1X, 1X, etc. IS-856 is also referred to as High Rate PacketData (HRPD), 1xEV-DO, etc. A TDMA system may implement a radiotechnology such as Global System for Mobile Communications (GSM). AnOFDMA system may implement a radio technology such as Evolved UTRA(E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.16 (WiMAX), IEEE802.20, Flash-OFDM®, etc. UTRA and E-UTRA are part of Universal MobileTelecommunication System (UMTS). Long Term Evolution (LTE) is anupcoming release of UMTS that uses E-UTRA. UTRA, E-UTRA, UMTS, LTE andGSM are described in documents from an organization named “3rdGeneration Partnership Project” (3GPP). cdma2000 and UMB are describedin documents from an organization named “3rd Generation PartnershipProject 2” (3GPP2).

FIG. 1 shows a wireless communication system 100, which may also bereferred to as an access network (AN) or a radio access network (RAN).System 100 may include a number of base stations 120. A base station isgenerally a fixed station that communicates with the wireless devicesand may also be referred to as a Node B, an evolved Node B, an accesspoint, etc. Each base station provides communication coverage for aparticular geographic area. In 3GPP, the term “cell” can refer to thecoverage area of a base station and/or a base station subsystem servingthis area, depending on the context in which the term is used. In 3GPP,the term “sector” can refer to the coverage area of a base stationand/or a base station subsystem serving this area.

A Base Station Controller (BSC) 122 may couple to a set of base stationsand provide coordination and control for these base stations. A MobileSwitching Center (MSC) 124 may couple to a set of BSCs and supportcommunication services for wireless devices. BSC 122 and MSC 124 mayalso be referred to by other names in other systems. System 100 mayinclude other network entities not shown in FIG. 1. A network entity 130may provide functionality to facilitate searches by wireless devices, asdescribed below. Network entity 130 may be a separate entity that maycouple to BSC 122 (as shown in FIG. 1), MSC 124, base stations 120,and/or other network entities. Network entity 130 may also be part of abase station, a BSC, an MSC, or some other network entity. Networkentity 130 may also be referred to as a central entity, a networkserver, etc.

Wireless devices 110 may be dispersed throughout the system, and eachwireless device may be stationary or mobile. A wireless device may alsobe referred to as a mobile station (MS), a user equipment (UE), aterminal, an access terminal, a subscriber unit, a station, etc. Awireless device may be a cellular phone, a personal digital assistant(PDA), a wireless modem, a handheld device, a laptop computer, etc. Awireless device may communicate with a base station on the forwardand/or reverse link to obtain communication services. In FIG. 1, a solidline with arrows at both ends may represent active communication betweena wireless device and a base station. A dashed line with an arrow at oneend may represent a wireless device searching for a signal.

A wireless device may have positioning capability and may receivesignals from satellites 140, which may be part of the United StatesGlobal Positioning System (GPS), the European Galileo system, theRussian GLONASS system, or a Global Navigation Satellite System (GNSS).The wireless device may measure signals from satellites 140 and obtainpseudo-range measurements for the satellites. Alternatively oradditionally, the wireless device may measure signals from base stations120 and obtain timing measurements for the base stations. Thepseudo-range measurements and/or timing measurements may be used toderive a location estimate for the wireless device.

A wireless device may search for signals from a system upon power up. Ifa system is found, then the wireless device may operate in either (i) aconnected mode and actively communicate with the system to obtaincommunication service or (ii) an idle mode and camp on the system ifcommunication is not required. The wireless device may fail to acquire asystem at power up (e.g., if the wireless device is in an area with noservice) or may lose an acquired system while in the idle or connectedmode (e.g., due to user mobility or radio link failure). The wirelessdevice may then enter an out-of-service state and search for signals.

The wireless device may periodically perform searches to detect for asignal while in the out-of-service state. A search may also be referredto as a scan, a system search, a cell search, signal re-acquisition,etc. A search may be performed in different manners for differentsystems, as described below.

FIG. 2 shows a design of periodically performing searches while in theout-of-service state. In this design, the wireless device may wake upevery scan period of T_(scan) _(—) _(period) seconds and perform asearch for T_(awake) seconds. The wireless device may sleep forT_(sleep) seconds after the awake period and may power down as muchcircuitry as possible while asleep in order to conserve battery power.Each scan period may thus include an awake/on period of T_(awake)seconds and a sleep/off period of T_(sleep). The scan period and scanrate may be given as:

T _(scan) _(—) _(period) =T _(awake) +T _(sleep), and  Eq (1)

R _(scan)=1/T _(scan) _(—) _(period),  Eq (2)

where R_(scan) is the scan rate.

In the design shown in FIG. 2, searches may be performed with a fixedawake period and a fixed scan period. In another design, searches may beperformed with a fixed awake period and a variable scan period. In yetanother design, searches may be performed with a variable scan periodand a fixed duty cycle for the awake period. For all designs, the scanrate and/or awake period may be selected based on a tradeoff betweenbattery life and signal re-acquisition performance. A faster scan rateand/or a longer awake period may be selected for faster signalre-acquisition. A slower scan rate and/or a shorter awake period may beselected for longer battery life.

The wireless device may perform searches in various manners while in theout-of-service state. In one design, which may be referred to as uniformsearches, the wireless device may perform searches at a fixed scan ratefor the entire duration of the out-of-service state. In another design,which may be referred to as telescopic searches, the wireless device mayperform searches at progressively slower scan rates while in theout-of-service state. For example, the wireless device may performsearches at an initial scan rate for the first X seconds, then performsearches at a slower scan rate for the next Y seconds, then performsearches at an even slower scan rate for the next Z seconds, etc. Forboth designs, the scan rate(s) and the awake period may be determined apriori (e.g., during the design phase of the wireless device) and may beused whenever the wireless device goes out of service. Usingpre-configured scan rate(s) and awake period may provide sub-optimalperformance in many scenarios.

In an aspect, the scan rate and/or some other parameters for searchesmay be determined based on one or more of the following:

-   -   Network information—any information related to the operational        characteristics of the system such as system loading, the number        of dropped calls, etc.,    -   Device information—any information related to the status of the        wireless device such as the amount of available battery, etc.,        and    -   Environmental information—any information that is not network        information or device information.

In general, any information that may be pertinent in determiningparameters for searches may be collected. The collected information maybe used to determine a single scan rate to use for uniform searches forthe entire duration of the out-of-service state. The collectedinformation may also be used to determine progressively slower scanrates for telescopic searches. In general, the collected information maybe used to determine one or more search parameters such as scan rate,awake time, sleep time, search duty cycle (which is the ratio of theawake time to the scan period), etc. For simplicity, the use of thecollected information to determine a scan rate is described below. Thisscan rate may be the single scan rate used for uniform searches for theentire duration of the out-of-service state, the initial scan rate amongthe progressively slower scan rates for telescopic searches, etc. Theslower scan rates may be determined based on the initial scan rate.

In one design, a wireless device may collect environmental and deviceinformation. The wireless device may use the collected information todetermine its scan rate. Alternatively or additionally, the wirelessdevice may send the collected information to network entity 130, whichmay use the collected information from many wireless devices todetermine the scan rate to use by the wireless devices.

The wireless device may collect some or all of the followingenvironmental information:

When (e.g., date and time) the wireless device goes out of service,

The location of the wireless device when it goes out of service,

When the wireless device re-acquires a signal,

The location of the wireless device when it re-acquires a signal,

Whether the wireless device is mobile or stationary when it goesout-of-service,

The duration of each out-of-service event,

How frequently the wireless device goes out-of-service, and

Signal strength, system identifier (ID), time, and location of thewireless device.

The out-of-service duration is the amount of time from when the wirelessdevice goes out of service to when the wireless device re-acquires asignal. The out-of-service duration may also be referred to asout-of-service time, re-acquisition time, etc.

The wireless device may collect some or all of the information listedabove, depending on its capability. For example, the location of thewireless device may be available if the wireless device has positioningcapability and may be unavailable otherwise. The location of thewireless device may have fine or coarse accuracy depending on thepositioning capability of the wireless device, e.g., fine accuracy forsatellite-based positioning and coarse accuracy for network-basedpositioning. The wireless device may also collect other types ofenvironmental information.

The wireless device may collect some or all of the following deviceinformation:

-   -   The amount of battery power available at the wireless device,    -   Whether the wireless device is in the connected mode or the idle        mode when it goes out of service, and    -   Whether the wireless device has a voice or data call when it        goes out of service.        The wireless device may also collect other types of device        information.

The wireless device may determine the scan rate based on the collectedinformation. The wireless device may also send the collected informationto network entity 130, e.g., after the wireless device re-acquires asignal. The wireless device may also aggregate the collected informationand send the information to network entity 130 at a convenient time,e.g., during off-peak hours. The wireless device may automaticallyreport the collected information to network entity 130 as a backgroundtask without requiring inputs from the user.

In another design, network entity 130 may collect information fromwireless devices and/or information from other network entities such asbase station 120, BSC 122, MSC 124, etc. In general, network entity 130may collect information for a designated area of any size. For example,the designated area may comprise the coverage area of a base station,the coverage area of a set of base stations, the coverage area of a BSC,the coverage area of an MSC, etc.

Network entity 130 may collect some or all of the followingenvironmental information:

-   -   The environmental information collected by the wireless devices,    -   How many wireless devices are out of service,    -   The durations of the out-of-service events encountered by the        wireless devices,    -   How often the wireless devices go out of service,    -   The locations of the wireless devices, e.g., before going out of        service and after re-acquiring a signal,    -   How many calls are dropped in the designated area, and    -   Weather conditions in the designated area.

The locations of the wireless devices may be determined by the wirelessdevices and reported to network entity 130. The locations of thewireless devices may also be determined based on reverse link signalssent by the wireless devices and measured by the base stations. Networkentity 130 may also collect other types of environmental information.

Network entity 130 may collect some or all of the following networkinformation:

Network loading in the designated area,

Types of calls made by wireless devices in the designated area,

Throughputs of the calls made by the wireless devices, and

Number of base stations in an active set of each wireless device.

Network entity 130 may also collect other types of network information.Network entity 130 may also collect device information from the wirelessdevices in the designated area.

In general, network entity 130 and/or a wireless device may determinethe scan rate based on various schemes or algorithms. Different schemesmay be used depending on the types of information available and thedesired optimization criteria, e.g., to extend battery life, to improvere-acquisition performance, or both. Several example schemes fordetermining the scan rate are described below.

In one design, the scan rate may be determined based on an averageout-of-service time. An entity (e.g., a wireless device or networkentity 130) may collect information on the duration of eachout-of-service event and may determine the average out-of-service time.For example, the wireless device may determine the duration of eachout-of-service event encountered by the wireless device and maydetermine the average out-of-service time for the wireless device.Network entity 130 may obtain the duration of each out-of-service eventencountered by wireless devices within the designated area and maydetermine the average out-of-service time for all wireless deviceswithin the designated area. The average out-of-service time may also beestimated based on environmental information, network information,and/or device information. In any case, the scan rate may be set basedon the average out-of-service time. In one design, if the averageout-of-service time is T seconds, then the scan rate may be equal to Tseconds or to η·T seconds, where η is a scaling factor that may bedependent on the desired optimization criterion. For example, η may be asmaller value (e.g., η<1) to improve re-acquisition performance or alarger value (e.g., η>1) to extend battery life.

The design described above determines the scan rate such that goodperformance (in terms of battery life and/or re-acquisition performance)can be obtained on average. Location information is not used indetermining the average out-of-service time and the scan rate. Thewireless device may determine the scan rate based on its averageout-of-service time and use this scan rate whenever it goes out ofservice. Network entity 130 may also determine the scan rate based onthe average out-of-service time for all wireless devices within thedesignated area and may provide this scan rate to the wireless devices.Each wireless device may then use the scan rate provided by networkentity 130 whenever that wireless device goes out of service.

In one design, the scan rate may be adaptively updated by network entity130 to improve re-acquisition performance and/or battery life. Networkentity 130 may determine a scan rate of R (e.g., R=once every 10seconds) based on the collected information, e.g., as described above.The wireless devices within the designated area may perform searches atthe scan rate of R determined by network entity 130.

The average re-acquisition time of the wireless devices may be dependenton (e.g., may be approximately equal to) the scan period, which isT=1/R. Network entity 130 may hypothesize that a higher scan rate mightimprove the average re-acquisition time. Network entity 130 may thendirect the wireless devices to use the higher scan rate of R_(higher1)(e.g., R_(higher1)=once every 5 seconds) in an attempt to decrease theaverage re-acquisition time. Network entity 130 may then collectinformation on the out-of-service durations and determine the averagere-acquisition time with the wireless devices using the higher scanrate. If the new average re-acquisition time is shorter than T, then thehigher scan rate improves the average re-acquisition time. Networkentity 130 may then use the higher scan rate of R_(higher1) instead ofthe original scan rate of R.

Network entity 130 may attempt to further improve the scan rate forfaster re-acquisition time. In the example above, if the averagere-acquisition time is close to 1/R_(higher1) with the higher scan rateof R_(higher1), then network entity 130 may select an even higher scanrate of R_(higher2), e.g., R_(higher2)=once every 2.5 seconds. Networkentity 130 may then collect information on the out-of-service durations,determine whether the higher scan rate of R_(higher2) improves theaverage re-acquisition time, and select the scan rate accordingly.Conversely, in the example above, if the average re-acquisition time isclose to T with the higher scan rate of R_(higher1), then network entity130 may select a scan rate between R_(higher1) and R, e.g.,R_(higher3)=once every 7.5 seconds. Network entity 130 may then collectinformation on the out-of-service durations, determine whether the scanrate of R_(higher3) improves the average re-acquisition time, and selectthe scan rate accordingly. Network entity 130 may iteratively adjust thescan rate (e.g., using a binary search or a linear search) until theaverage re-acquisition time no longer improves or is adequate.

In another design, a coverage map may be determined based on thecollected information and may be used to determine the scan rate.Network entity 130 may obtain the locations of the wireless devices, theout-of-service durations, and/or other information when the wirelessdevices go out of service. Network entity 130 may identify areas of goodcoverage with short out-of-service durations and areas of poor coveragewith long out-of-service durations. Network entity 130 may determinesuitable scan rates for different areas based on the averageout-of-service durations for these areas. Network entity 130 may providethe scan rate for each area to wireless devices located within thatarea. Each wireless device may perform searches based on the scan rateapplicable for its current location.

In another design, additional information may be used to further refinethe scan rate. The scan rate may be a function of one or more types ofinformation collected by network entity 130. Network entity 130 mayobtain the out-of-service durations, network loading, weatherconditions, time of day, and/or other information when the wirelessdevices go out of service. Network entity 130 may determine the scanrate for different values of the collected information. For example,network entity 130 may determine the average out-of-service time fordifferent weather conditions such as sunny, cloudy, rainy, etc. Networkentity 130 may then determine the scan rate for each weather conditionbased on the average out-of-service time for that weather condition.Network entity 130 may provide the scan rate for the current weathercondition to the wireless devices.

In general, network entity 130 may determine the scan rate based on afunction of any type of information or any combination of information.For example, network entity 130 may determine the scan rate based on afunction of network loading, a function of time of day, etc. Thefunction(s) for scan rate versus different types of information may beimplemented with look-up tables, linear and/or non-linear equations,etc. Network entity 130 may provide the appropriate scan rate to thewireless devices based on the current operating conditions for thewireless devices.

In another design, different scan rates may be defined for differentoptimization criteria. For example, a faster scan rate of R_(fast) maybe used for faster re-acquisition time, a slower scan rate of R_(slow)may be used to extend battery life, and a nominal scan rate of R_(nom)may be used for both, where R_(Slow)<R_(nom)<R_(fast). One scan rate(e.g., R_(nom)) may be determined based on the collected information.The other scan rates (e.g., R_(fast) and R_(slow)) may be a function ofthe determined scan rate. A wireless device may use a suitable scan ratedepending on the desired performance. For example, the wireless devicemay use the slower scan rate of R_(slow) when its battery is low or whenit goes out of service in the idle mode. The wireless device may use thefaster scan rate of R_(fast) when its battery is fully charged or whenit goes out of service in the connected mode.

In general, the various designs described above for determining the scanrate may be performed by network entity 130 and/or by a wireless device.Network entity 130 may determine the scan rate based on collectedinformation for all wireless devices within the designated area coveredby network entity 130. Network entity 130 may provide the scan rate tothe wireless devices, e.g., when they enter the designated area. Networkentity 130 may also update the scan rate, e.g., as described above, andmay provide the updated scan rate to the wireless devices at any timewhile these wireless devices are serviced by network entity 130. Awireless device may receive the scan rate from network entity 130 whilethe wireless device is in service, store the scan rate, and performsearches in accordance with the scan rate at a later time when thewireless device goes out of service.

A wireless device may determine its scan rate based on informationcollected by the wireless device. In one design, the wireless device mayperform searches based on the scan rate determined by the wirelessdevice. In another design, the wireless device may determine a scan rateof R_(wd) based on its collected information and may also receive a scanrate of R_(ne) determined by network entity 130 based on collectedinformation for wireless devices within the designated area. In onedesign, the wireless device may determine a final scan rate of R_(final)based on its computed scan rate and the received scan rate, as follows:

R _(final)=α_(wd) ·R _(wd)+α_(ne) ·R _(ne),  Eq (3)

-   where α_(wd) is a weight for the scan rate determined by the    wireless device, and α_(ne) is a weight for the scan rate received    from network entity 130.

Each weight may have a value within a range of 0 to 1. A larger value ofα_(wd) may be used to give more weight to the scan rate determined bythe wireless device. A larger value of αne may be used to give moreweight to the scan rate determined by network entity 130. The weightsmay be constrained such that α_(wd)+α_(ne)=1. The wireless device mayperform searches based on the final scan rate.

In one design, which may be referred to as fixed rate scanning, a scanrate may be obtained for a wireless device at a predetermined time. Thisscan rate may be determined by the wireless device, provided by networkentity 130, or derived based on the scan rate determined by the wirelessdevice and the scan rate provided by the network entity, as describedabove. The wireless device may use this scan rate for the entireduration in which it is within the designated area and serviced bynetwork entity 130.

In another design, which may be referred to as variable rate scanning,the scan rate for the wireless device may be changed by network entity130 and/or the wireless device. The change in the scan rate may occur atany time while the wireless device is within the designated area andcovered by network entity 130.

For clarity, the techniques have been specifically described above fordetermining the scan rate for searches. The techniques may also be usedto determine (i) other search parameters such as awake time, sleep time,etc., (ii) signal processing parameters such as coherent accumulationtime, non-coherent accumulation time, etc., and/or (iii) otherparameters applicable for searches.

For clarity, the techniques have been specifically described above forsearches performed by a wireless device when it is out of service andnot receiving a suitable signal from any base station. The techniquesmay also be used to determine search parameters for other types ofsearches such as searches for signals from other systems or radiotechnologies (i.e., inter-system searches), searches for signals onother frequency channels (i.e., inter-frequency searches), searches forsignals from other cells, etc. The term “out of service” may thusencompass any of the scenarios described above and may refer to beingout of service with respect to another system, another radio technology,another frequency channel, another cell, etc.

FIG. 3 shows a design of a process 300 for supporting searches forsignals in a wireless communication system. Process 300 may be performedby network entity 130 (as described below) or by some other entity.Network entity 130 may collect information for a plurality of wirelessdevices (block 312). The collected information may compriseout-of-service durations, locations of wireless devices, frequency ofout-of-service events, network loading, dropped calls, weatherconditions, other types of information given above, or a combinationthereof. Network entity 130 may receive the information from theplurality of wireless devices and/or from at least one other networkentity, e.g., base stations 120, BSC 122, MSC 124, etc.

Network entity 130 may determine at least one search parameter based onthe collected information (block 314). In one design, the at least onesearch parameter may comprise a scan rate corresponding to a rate forperforming searches. In another design, the at least one searchparameter may comprise (i) a first scan rate to use in performingsearches when longer battery life is desired and (ii) a second scan rateto use in performing searches when faster signal re-acquisition isdesired, with the second scan rate being faster than the first scanrate. The at least one search parameter may comprise other parameters,as described above.

In one design of block 314, network entity 130 may estimate an averageout-of-service time for the plurality of wireless devices based on thecollected information. Network entity 130 may then determine a scan ratebased on the estimated average out-of-service time. Network entity 130may also adjust the scan rate, determine an updated averageout-of-service time with the adjusted scan rate, and use the adjustedscan rate if the updated average out-of-service time is improved over(i.e., shorter than) the estimated average out-of-service time. Networkentity 130 may iteratively adjust the scan rate until a terminationcondition is encountered, which may occur when the averageout-of-service time is acceptable or cannot be further improved. Networkentity 130 may then use the scan rate obtained when the terminationcondition is encountered.

In another design of block 314, network entity 130 may determine acoverage map based on the collected information for the plurality ofwireless devices. The coverage map may be obtained by identifying areasof poor coverage with long average out-of-service time and areas of goodcoverage with short average out-of-service time. These different areasmay be identified based on the out-of-service durations and thelocations of the plurality of wireless devices, which may be provided bythe collected information. The average out-of-service time may be deemedto be long if it exceeds a first threshold or short if it is less than asecond threshold, with the thresholds being suitably selected values.Network entity 130 may determine at least one scan rate for at least onearea based on the coverage map. For example, the areas of poor coveragemay be associated with slower scan rates, and the areas of good coveragemay be associated with faster scan rates.

Network entity 130 may provide the at least one search parameter towireless devices for use in performing searches for signals when thewireless devices are out of service (block 316). Network entity 130 maycollect information for wireless devices located within a designatedarea and may provide the at least one search parameter to wirelessdevices located within the designated area.

FIG. 4 shows a design of an apparatus 400 for supporting searches forsignals. Apparatus 400 includes a module 412 to collect information fora plurality of wireless devices, a module 414 to determine at least onesearch parameter (e.g., a scan rate) based on the collected information,and a module 416 to provide the at least one search parameter towireless devices for use in performing searches for signals when thewireless devices are out of service.

FIG. 5 shows a design of a process 500 for operating a wireless device.The wireless device may collect information related to out-of-serviceevents encountered by the wireless device (block 512). The collectedinformation may comprise out-of-service durations, locations of thewireless device, frequency of out-of-service events, signal strength,any of the information described above, or a combination thereof. Thewireless device may send the collected information to a network entityfor use in determining at least one search parameter (block 514). Thewireless device may receive the at least one search parameter determinedby the network entity based on information collected by the networkentity for a plurality of wireless devices (block 516). The wirelessdevice may thereafter perform searches for signals in accordance withthe at least one search parameter when the wireless device is out ofservice (block 518).

The at least one search parameter may comprise a scan rate to use forthe entire duration in which the wireless device is covered by thenetwork entity. Alternatively, the at least one search parameter maycomprise a scan rate that is changeable by the network entity during thetime in which the wireless device is covered by the network entity. Inany case, the wireless device may perform searches at the scan rate whenit is out of service. In one design, the wireless device may determineits current operating conditions, e.g., its location, received signalstrength, operating mode, available battery power, etc. The wirelessdevice may adjust the scan rate based on its current operatingconditions and may perform searches at the adjusted scan rate.

FIG. 6 shows a design of an apparatus 600 for operating a wirelessdevice. Apparatus 600 includes a module 612 to collect informationrelated to out-of-service events encountered by the wireless device, amodule 614 to send the collected information to a network entity, amodule 616 to receive at least one search parameter determined by thenetwork entity based on information collected by the network entity fora plurality of wireless devices, and a module 618 to perform searchesfor signals in accordance with the at least one search parameter whenthe wireless device is out of service.

FIG. 7 shows a design of a process 700 for operating a wireless device.The wireless device may collect information related to out-of-serviceevents encountered by the wireless device, e.g., the informationdescribed above for FIG. 5 (block 712). The wireless device maydetermine at least one search parameter based on the collectedinformation (block 714). The wireless device may perform searches forsignals in accordance with the at least one search parameter when it isout of service (block 716).

In one design of block 714, the wireless device may estimate an averageout-of-service time for the wireless device based on the collectedinformation. The wireless device may then determine a scan rate based onthe estimated average out-of-service time. In one design, the wirelessdevice may determine its current operating conditions, e.g., itslocation, received signal strength, operating mode, available batterypower, etc. The wireless device may determine the scan rate basedfurther on its current operating conditions.

In one design, the wireless device may determine a first scan rate basedon the collected information and may receive a second scan rate from anetwork entity. The wireless device may determine a third scan ratebased on the first and second scan rates. The wireless device may thenperform searches in accordance with the third scan rate when it is outof service.

FIG. 8 shows a design of an apparatus 800 for operating a wirelessdevice. Apparatus 800 includes a module 812 to collect informationrelated to out-of-service events encountered by the wireless device, amodule 814 to determine at least one search parameter based on thecollected information, and a module 816 to perform searches for signalsin accordance with the at least one search parameter when the wirelessdevice is out of service.

The modules in FIGS. 4, 6 and 8 may comprise processors, electronicsdevices, hardware devices, electronics components, logical circuits,memories, etc., or any combination thereof.

A wireless device may perform a search in different manners fordifferent systems or radio technologies. For a search in WCDMA, thewireless device may perform one or more frequency scans to detect forstrong frequency channels in a frequency band. The wireless device maythen attempt acquisition on each strong frequency channel, e.g., using athree-step process. In step one, the wireless device may search for a256-chip primary synchronization code (PSC) sent on a primarysynchronization channel (SCH) by correlating a received signal at thewireless device with a locally generated PSC at different time offsets.The wireless device may use the PSC to detect for the presence of a celland to ascertain slot timing of that cell. In step two, the wirelessdevice may determine a pattern of secondary synchronization codes (SSCs)used by each cell for which the PSC has been detected. The wirelessdevice can determine frame timing and a scrambling code group used for acell based on the detected SSC pattern for that cell. In step three, thewireless device may determine the scrambling code used by each cell forwhich the SSC pattern has been detected. Each SSC pattern is associatedwith a group of eight scrambling codes. The wireless device may evaluateeach of the eight scrambling codes to determine which scrambling code isused by the cell.

For a search in GSM, the wireless device may perform a power scan tomeasure received power of each radio frequency (RF) channel in afrequency band and may identify strong RF channels. The wireless devicemay then attempt acquisition on each strong RF channel by (i) detectingfor a tone sent on a frequency correction channel (FCCH), (ii) decodinga burst sent on a synchronization channel (SCH) to obtain a basetransceiver station identity code (BSIC) for a GSM cell, and (iii)decoding a broadcast control channel (BCCH) to obtain systeminformation.

For a search in 1X or HRPD, the wireless device may search for pilots ondifferent frequency channels, e.g., on one or more most recently usedfrequency channels and/or one or more frequency channels in a preferredroaming list (PRL). The wireless device may then attempt acquisition oneach frequency channel in which pilot is detected.

In one design, the wireless device may complete a search prior to goingto sleep. In this design, the awake period may be variable and may bedependent on various factors such as the number of frequency channelsdetected, the received signal strength, etc. In another design, thewireless device may perform a search for a fixed awake period. If thesearch is not completed during the awake period, then state informationfor the search may be saved, and the search may be resumed in the nextawake period.

FIG. 9 shows a block diagram of a design of wireless device 110, basestation 120, and network entity 130 in FIG. 1. At wireless device 110, amodem processor 924 may receive data to be sent by the wireless device,process (e.g., encode and modulate) the data, and generate output chips.A transmitter (TMTR) 932 may condition (e.g., convert to analog, filter,amplify, and frequency upconvert) the output chips and generate areverse link signal, which may be transmitted via an antenna 934. On theforward link, antenna 934 may receive forward link signals from basestation 120 and/or other base stations. A receiver (RCVR) 936 maycondition (e.g., filter, amplify, frequency downconvert, and digitize)the received signal from antenna 934 and provide samples. Modemprocessor 924 may process (e.g., demodulate and decode) the samples andprovide decoded data. Modem processor 924 may also perform searches inaccordance with a suitable scan rate when wireless device 110 is out ofservice. Modem processor 924 may perform processing and searches inaccordance with a radio technology (e.g., CDMA 1X, HRPD, WCDMA, GSM,etc.) utilized by the system.

A controller/processor 920 may direct the operation at wireless device110. Controller/processor 920 may perform or direct process 500 in FIG.5, process 700 in FIG. 7, and/or other processes for the techniquesdescribed herein. Controller/processor 920 may also collect informationrelated to out-of-service events encountered by wireless device 110. Amemory 922 may store program codes and data for wireless device 110.Memory 922 may also store the collected information, which may be usedby controller/processor 920 to determine a scan rate and/or may be sentto network entity 130. A digital signal processor 926 may performvarious types of processing for wireless device 110. Processors 920, 924and 926 and memory 922 may be implemented on an application specificintegrated circuit (ASIC) 910. Memory 922 may also be implementedexternal to the ASIC.

At base station 120, transmitter/receiver (TMTR/RCVR) 946 may supportradio communication with wireless device 110 and/or other wirelessdevices. A controller/processor 940 may perform various functions forcommunication with the wireless devices. Controller/processor 940 mayalso perform or direct process 300 in FIG. 3 and/or other processes forthe techniques described herein. Controller/processor 940 may alsocollect information for wireless devices served by base station 120,e.g., the environment and network information described above. A memory942 may store program codes and data for base station 120. Memory 942may also store the collected information, which may be used bycontroller/processor 940 to determine a scan rate and/or may be sent tonetwork entity 130. A communication (Comm) unit 944 may supportcommunication with other network entities, e.g., network entity 130. Ingeneral, base station 120 may include any number of controllers,processors, memories, transmitters, receivers, communication units, etc.

At network entity 130, a controller/processor 950 may perform variousfunctions to support searches by the wireless devices.Controller/processor 950 may perform or direct process 300 in FIG. 3and/or other processes for the techniques described herein. A memory 952may store program codes and data for network entity 130. Memory 952 mayalso store collected information, which may be received from thewireless devices, base stations, and/or other network entities.Controller/processor 950 may determine the scan rate and/or other searchparameters based on the collected information. A communication unit 954may support communication with other network entities, e.g., basestation 120, BSC 122, MSC 124, etc. In general, network entity 130 mayinclude any number of controllers, processors, memories, communicationunits, etc.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, circuits, and algorithm steps described inconnection with the disclosure herein may be implemented as electronichardware, computer software, or combinations of both. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, circuits, and steps have beendescribed above generally in terms of their functionality. Whether suchfunctionality is implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure.

The various illustrative logical blocks, modules, and circuits describedin connection with the disclosure herein may be implemented or performedwith a general-purpose processor, a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described herein. Ageneral-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm described in connection with thedisclosure herein may be embodied directly in hardware, in a softwaremodule executed by a processor, or in a combination of the two. Asoftware module may reside in RAM memory, flash memory, ROM memory,EPROM memory, EEPROM memory, registers, hard disk, a removable disk, aCD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal. In the alternative, theprocessor and the storage medium may reside as discrete components in auser terminal.

In one or more exemplary designs, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by ageneral purpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that can be used to carryor store desired program code means in the form of instructions or datastructures and that can be accessed by a general-purpose orspecial-purpose computer, or a general-purpose or special-purposeprocessor. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

The previous description of the disclosure is provided to enable anyperson skilled in the art to make or use the disclosure. Variousmodifications to the disclosure will be readily apparent to thoseskilled in the art, and the generic principles defined herein may beapplied to other variations without departing from the scope of thedisclosure. Thus, the disclosure is not intended to be limited to theexamples and designs described herein but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

1. A method of supporting searches for signals in a wirelesscommunication system, comprising: collecting information for a pluralityof wireless devices; determining at least one search parameter based onthe collected information; and providing the at least one searchparameter to wireless devices for use in performing searches for signalswhen the wireless devices are out of service.
 2. The method of claim 1,wherein the collecting information comprises collecting information onout-of-service durations, locations of wireless devices, frequency ofout-of-service events, network loading, dropped calls, weatherconditions, or a combination thereof.
 3. The method of claim 1, furthercomprising: receiving the information for the plurality of wirelessdevices from the plurality of wireless devices, or from at least onenetwork entity, or both.
 4. The method of claim 1, wherein the at leastone search parameter comprises a scan rate corresponding to a rate forperforming searches.
 5. The method of claim 1, wherein the at least onesearch parameter comprises a first scan rate to use in performingsearches when longer battery life is desired, and a second scan rate touse in performing searches when faster signal re-acquisition is desired,the second scan rate being faster than the first scan rate.
 6. Themethod of claim 1, wherein the determining the at least one searchparameter comprises estimating an average out-of-service time for theplurality of wireless devices based on the collected information, anddetermining a scan rate based on the estimated average out-of-servicetime.
 7. The method of claim 6, wherein the determining the at least onesearch parameter further comprises adjusting the scan rate, determiningan updated average out-of-service time with the adjusted scan rate, andusing the adjusted scan rate if the updated average out-of-service timeis improved over the estimated average out-of-service time.
 8. Themethod of claim 7, wherein the determining the at least one searchparameter further comprises iteratively performing the adjusting thescan rate and the determining the updated average out-of-service timeuntil a termination condition is encountered, and using a final adjustedscan rate obtained when the termination condition is encountered.
 9. Themethod of claim 1, wherein the determining the at least one searchparameter comprises determining a coverage map based on the collectedinformation for the plurality of wireless devices, and determining atleast one scan rate for at least one area based on the coverage map. 10.The method of claim 9, wherein the determining the coverage mapcomprises obtaining out-of-service durations and locations of theplurality of wireless devices from the collected information, andidentifying areas of poor coverage with long out-of-service time andareas of good coverage with short out-of-service time based on theout-of-service durations and the locations of the plurality of wirelessdevices.
 11. The method of claim 10, wherein the areas of poor coverageare associated with scan rates slower than scan rates for areas of goodcoverage.
 12. The method of claim 1, wherein the collecting informationcomprises collecting information for the plurality of wireless deviceslocated within a designated area, and wherein the providing the at leastone search parameter comprises providing the at least one searchparameter to wireless devices located within the designated area.
 13. Anapparatus supporting searches for signals, comprising: at least oneprocessor configured to collect information for a plurality of wirelessdevices, to determine at least one search parameter based on thecollected information, and to provide the at least one search parameterto wireless devices for use in performing searches for signals when thewireless devices are out of service.
 14. The apparatus of claim 13,wherein the at least one processor is configured to collect informationon out-of-service durations, locations of wireless devices, frequency ofout-of-service events, network loading, dropped calls, weatherconditions, or a combination thereof.
 15. The apparatus of claim 13,wherein the at least one processor is configured to estimate an averageout-of-service time for the plurality of wireless devices based on thecollected information, and to determine a scan rate based on theestimated average out-of-service time.
 16. The apparatus of claim 15,wherein the at least one processor is configured to adjust the scanrate, to determine an updated average out-of-service time with theadjusted scan rate, and to use the adjusted scan rate if the updatedaverage out-of-service time is improved over the estimated averageout-of-service time.
 17. The apparatus of claim 13, wherein the at leastone processor is configured to determine a coverage map based on thecollected information for the plurality of wireless devices, and todetermine at least one scan rate for at least one area based on thecoverage map.
 18. An apparatus supporting searches for signals,comprising: means for collecting information for a plurality of wirelessdevices; means for determining at least one search parameter based onthe collected information; and means for providing the at least onesearch parameter to wireless devices for use in performing searches forsignals when the wireless devices are out of service.
 19. The apparatusof claim 18, wherein the means for collecting information comprisesmeans for collecting information on out-of-service durations, locationsof wireless devices, frequency of out-of-service events, networkloading, dropped calls, weather conditions, or a combination thereof.20. The apparatus of claim 18, wherein the means for determining the atleast one search parameter comprises means for estimating an averageout-of-service time for the plurality of wireless devices based on thecollected information, and means for determining a scan rate based onthe estimated average out-of-service time.
 21. The apparatus of claim18, wherein the means for determining the at least one search parametercomprises means for determining a coverage map based on the collectedinformation for the plurality of wireless devices, and means fordetermining at least one scan rate for at least one area based on thecoverage map.
 22. A computer program product, comprising: acomputer-readable medium comprising: code for causing at least onecomputer to collect information for a plurality of wireless devices;code for causing the at least one computer to determine at least onesearch parameter based on the collected information; and code forcausing the at least one computer to provide the at least one searchparameter to wireless devices for use in performing searches for signalswhen the wireless devices are out of service.
 23. The computer programproduct of claim 22, wherein the computer-readable medium furthercomprises: code for causing the at least one computer to estimate anaverage out-of-service time for the plurality of wireless devices basedon the collected information; and code for causing the at least onecomputer to determine a scan rate based on the estimated averageout-of-service time.
 24. The computer program product of claim 22,wherein the computer-readable medium further comprises: code for causingthe at least one computer to determine a coverage map based on thecollected information for the plurality of wireless devices; and codefor causing the at least one computer to determine at least one scanrate for at least one area based on the coverage map.
 25. A method ofoperating a wireless device, comprising: receiving at least one searchparameter determined by a network entity based on information collectedby the network entity for a plurality of wireless devices; andperforming searches for signals in accordance with the at least onesearch parameter when the wireless device is out of service.
 26. Themethod of claim 25, further comprising: collecting information relatedto out-of-service events encountered by the wireless device; and sendingthe collected information to the network entity for use in determiningthe at least one search parameter.
 27. The method of claim 25, whereinthe at least one search parameter comprises a scan rate, the methodfurther comprising: determining current operating conditions of thewireless device; and adjusting the scan rate based on the currentoperating conditions, and wherein searches are performed in accordancewith the adjusted scan rate
 28. The method of claim 25, wherein the atleast one search parameter comprises a scan rate to use for entireduration in which the wireless device is covered by the network entity,and wherein searches are performed at the scan rate.
 29. The method ofclaim 25, wherein the at least one search parameter comprises a scanrate changeable by the network entity during duration in which thewireless device is covered by the network entity, and wherein searchesare performed at the scan rate.
 30. An apparatus for wirelesscommunication, comprising: at least one processor configured to receiveat least one search parameter determined by a network entity based oninformation collected by the network entity for a plurality of wirelessdevices, and to perform searches for signals in accordance with the atleast one search parameter when a wireless device is out of service. 31.The apparatus of claim 30, wherein the at least one processor isconfigured to collect information related to out-of-service eventsencountered by the wireless device, and to send the collectedinformation to the network entity for use in determining the at leastone search parameter.
 32. The apparatus of claim 30, wherein the atleast one processor is configured to receive a scan rate from thenetwork entity, to determine current operating conditions of thewireless device, to adjust the scan rate based on the current operatingconditions, and to perform searches in accordance with the adjusted scanrate.
 33. A method of operating a wireless device, comprising:collecting information related to out-of-service events encountered bythe wireless device; determining at least one search parameter based onthe collected information; and performing searches for signals inaccordance with the at least one search parameter when the wirelessdevice is out of service.
 34. The method of claim 33, wherein thecollecting information comprises collecting information onout-of-service durations, locations of the wireless device, frequency ofout-of-service events, signal strength, or a combination thereof. 35.The method of claim 33, wherein the determining the at least one searchparameter comprises determining current operating conditions of thewireless device, and determining the at least one search parameter basedfurther on the current operating conditions.
 36. The method of claim 33,wherein the determining the at least one search parameter comprisesestimating an average out-of-service time for the wireless device basedon the collected information, and determining a scan rate based on theestimated average out-of-service time.
 37. The method of claim 33,wherein the at least one search parameter comprises a first scan ratedetermined based on the collected information, the method furthercomprising: receiving a second scan rate determined by a network entitybased on information collected by the network entity for a plurality ofwireless devices; and determining a third scan rate based on the firstand second scan rates, and wherein searches are performed in accordancewith the third scan rate when the wireless device is out of service. 38.An apparatus for wireless communication, comprising: at least oneprocessor configured to collect information related to out-of-serviceevents encountered by a wireless device, to determine at least onesearch parameter based on the collected information, and to performsearches for signals in accordance with the at least one searchparameter when the wireless device is out of service.
 39. The apparatusof claim 38, wherein the at least one processor is configured to collectinformation on out-of-service durations, locations of the wirelessdevice, frequency of out-of-service events, signal strength, or acombination thereof.
 40. The apparatus of claim 38, wherein the at leastone processor is configured to determine current operating conditions ofthe wireless device, and to determine the at least one search parameterbased further on the current operating conditions.
 41. The apparatus ofclaim 38, wherein the at least one processor is configured to estimatean average out-of-service time for the wireless device based on thecollected information, and to determine a scan rate based on theestimated average out-of-service time.
 42. The apparatus of claim 38,wherein the at least one processor is configured to determine a firstscan rate based on the collected information, to receive a second scanrate determined by a network entity based on information collected bythe network entity for a plurality of wireless devices, to determine athird scan rate based on the first and second scan rates, and to performsearches in accordance with the third scan rate when the wireless deviceis out of service.